A gate driver on array circuit is abbreviated as a GOA circuit. GOA circuits use the existing TFT-LCD (Thin Film Transistor-Liquid Crystal Display) array process technology to manufacture a gate-line scan driving signal circuit on an array substrate that implements a driving method of progressively scanning the gate.
Presently, oxide semiconductor thin film transistors receive more and more attention for their good electrical properties, and the integration of an oxide semiconductor thin film transistor into a driving circuit of a liquid crystal display is thus applied more widely. For oxide semiconductor thin film transistors, due to their electrical properties, the threshold voltage is sometimes less than 0V.
A structural diagram of an existing Nth-level GOA unit is illustrated in FIG. 1, which mainly comprises: a pull-up control unit 101, a pull-up unit 102, a pull-down unit 103, and a pull-down control unit 104. In the actual practice process, the pull-down unit 103 has an obvious electrical leakage phenomenon. A drain input signal of a TFT 11 is ST (N−2). A gate input signal of a TFT T41 and T31 is G(N+2). A drain input clock signal of a TFT T21 and a TFT T22 is CK(n). An output signal of a first output end is G(N). An output signal of a second output end is ST(N). A pull-down point Q(N), a low-level input end (VSS1), the TFT T43, the TFT T33, and signals LC1 and LC2 of the low-level input end belong to the pull-down control unit. Since the specific structure of the pull-down control unit 104 has been recorded in the existing technology, the detailed description thereof is omitted here.
As illustrated in FIG. 2, STV represents a starting signal of the GOA circuit. CK1-CK4 represent clock signals comprised in the GOA circuit. G1-G4 represent signals of first output ends of the 1st-4th-level GOA units. A clock signal period of a next level GOA unit has a 1/4 period overlap with a clock signal period of a previous level GOA unit. The duty ratios of the clock signals are both 50/50. When the TFT T21 is closed, the gate of the TFT T21 is connected to VSS1, and the source is connected to VSS1, so that VGS=0V. There is a larger problem of electrical leakage when the threshold voltage of the TFT is less than 0V.
As a result, it is necessary to provide a GOA circuit and a liquid crystal display device to solve the problems existing in the conventional technologies.